Multiple roles of palladium-coated magnetic anisotropic particles as catalysts, catalyst supports, and micro-stirrers

We report the external field-guided shape transformation of magnetite-polymer composite particles that play multiple roles in heterogeneous chemical reactions, such as catalysts, catalyst supports, and micro-stirrers. A microfluidic method was used to generate monodispersed emulsion droplets composed of polystyrene, magnetite nanoparticles (MNPs), and chloroform. While the solvent in the droplets was dried in the presence of an external magnetic field, the emulsion droplets were deformed or elongated along the field direction, consequently leading to magnetically responsive particles with anisotropic shape after complete removal of the solvent. Coarsegrained molecular dynamic simulations demonstrated that the shape deformation was due to destabilization of the MNPs upon solvent drying and migration of the aggregated MNPs in the polymer matrix along the external field. The particle shape could be readily tunable by modulating the field strength and direction as well as the concentrations of the MNPs and polymer. We further revealed that these magnetic anisotropic particles coated with palladium nanoparticles could be used as catalysts, catalyst supports, micro-stirrers when the particles were dispersed in a small confined volume of a catalytic precursor solution.